The invention relates to a centrifugal clutch and method of producing same, and, more particularly, to a clutch with a driving inner runner carrying on its circumference a plurality of resilient clutch elements made in one piece with a rotating ring which moves radially outwards with increasing speed and, at clutch speed, bear against the inner surface of a drum-shaped outer ring.
A centrifugal clutch is disclosed in German Utility Model 1,883,236. In this known centrifugal clutch, the radial forces acting on the clutch elements consist exclusively of centrifugal forces. The process of engaging and disengaging the clutch lasts a relatively long time, especially at high clutch speeds of over approximately 20,000 revolutions per minute, that is to say, far above the maximum speeds of normal reciprocating internal combustion engines. This results in high wear in the friction surfaces. A further result is that the speeds for the full engagement and disengagement of the clutch cannot be fixed sufficiently accurately.
U.S. Pat. No. 4,117,918 discloses the use of a roller member running up onto an inclined face for supporting the centrifugal forces of the clutch elements. The motion of the clutch elements necessary for this arrangement, however, in the peripheral direction requires a disadvantageous sliding application of springs, which results in an unsatisfactory accuracy for the radial restoring forces acting on the clutch elements. Moreover, although it was known to load the roller members by use of tension springs supported at the clutch elements, substantial additional expenses are undesirably incurred by the need to use two tension springs per clutch element and a bearing cage.
Further, U.S. Pat. No. 3,008,313 discloses a clutch, with particular application for injection pumps, in which the assistance of rolling members supported at inclined faces is enlisted to enable a sight angular adjustment between an input shaft and an output shaft depending upon the speed, although no clutching process takes place.
U.S. Pat. No. 4,140,210 discloses an arrangement whose purpose is to reduce friction between clutch elements and a runner, but does so by inclining the entire clutch element. This construction involves additional and thus undesirable expenses for constructing recesses in the inner runner.
It is an object of the invention to construct a centrifugal clutch of the aforementioned type which, especially when it is used at high speeds such as occur, for example, in connection with the operation of turbines driven by exhaust gas, assure low-wear operation and fixing of the speeds of engagement and disengagement of the clutch in a narrow tolerance band.
This objection has been achieved in a centrifugal clutch according to the present invention by providing a ring which forms, with the clutch elements, an intermediate runner. The ring is fastened to the inner runner in such a way that upon fixing in the radial direction a relative motion in the peripheral direction is possible by a slight amount. Rolling members, such as rollers and balls, are supported on flat or curved inclined faces of the inner runner which rise counter to the direction of the rotation of the inner runner and are arranged between the clutch elements and the inner runners.
The centrifugal clutch construction according to the invention greatly increases the radial forces acting on each clutch element at the start of clutching so that the frictional forces which commence at the instant and act upon the clutch elements cause displacement of the clutch elements in the peripheral direction. This displacement is enabled by the separation of the inner runners and the intermediate runners and by the specified type of fastening of the ring to the inner runner. The rolling members are caused to run up onto the inclined faces. This support offered to the centrifugal forces of the clutch elements by the radial forces exerted by the rolling members shortens the clutching process up to complete, non-slip clutching, whereby the clutch speed can also be more accurately fixed.
The present invention employs simple yet reliable fastening of the ring to a radial surface of the inner runner which forms a shoulder. Resilient connections of the clutch elements to the ring in such a way to permit tilting of the clutch elements about these connections in accordance with the present invention permit a stiff configuration of each clutch element, thus enabling a simultaneous application of the entire outer surface of each clutch element to the outer runner. Weakening of the necking material in the connection between each clutch element and ring allows the spring characteristics to be varied during production and thus accurately adjusted to specific requirements.
The present invention also provides a centrifugal clutch on which the rolling members are loaded in a direction on which the inclined faces are caused to rise by a spring supported on radial faces of the inner runner. This arrangement guarantees application of the rolling members both to the clutch elements and also to the inclined surfaces without play and with a cage being necessary for the rolling members.
According to yet another feature of the present invention, an oil-peeling nose formed by the end face of each clutch element is curved forward in its radially outward region peels off any oil film present on the inner surface of the runner when the nose approaches the outer runner, whereby the friction coefficient and hence the clutching forces between outer and intermediate runner are increased.
The present invention further provides that in the region of each clutch element, rearward and with respect to the direction of rotation of the inner runners, the outer surface of the clutch element is reduced radially inward and forms and acute angle with respect to the peripheral directions. Thus, when the speed of the outer runner is higher by comparison between the inner and the outer runner, an oil wedge is formed between the clutch elements and the outer runner and reduces the friction between these parts and thus delays braking of the outer runner.
The method for producing the centrifugal clutch in accordance with the present invention involves constructing an annular body as an intermediate runner, and machining the outer surfaces of the clutch elements and/or the inner surface of the outer runner to size at clutch engagement speed. This guarantees accurate maintenance of the radial dimensions of the clutch elements and the outer runner which appear with the clutch speed and are extremely important for the clutching and declutching process, even if, due to differences in manufacture and irregularities in the material, slight differences should result in the masses and spring characteristics of the individual clutch elements. Moreover, it is possible by virtue of the present invention to machine the intermediate runner which is separate from the inner runner.